Process Simulation of a 620 Mw-Natural Gas Combined Cycle Power Plant with Optimum Flue Gas Recirculation

Ahmed Badr Al Hashmi,Abdel Aziz Abdulla Mohamed,Zin Eddine Dadach

doi:10.4236/ojee.2018.72003

Ahmed Badr Al Hashmi, Abdel Aziz Abdulla Mohamed + Show 1 more

Open Access

https://doi.org/10.4236/ojee.2018.72003

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Abstract

The main objective of this investigation is to obtain an optimum value for the flue gas recirculation ratio in a 620 MW-Natural Gas Combined Cycle (NGCC) power plant with a 100% excess air in order to have a composition of the exhaust gas suitable for an effective absorption by amine solutions. To reach this goal, the recirculated flue gas is added to the secondary air (dilution air) used for cooling the turbine. The originality of this work is that the optimum value of a Flue Gas Recirculation (FGR) ratio of 0.42 is obtained from the change of the slope related to the effects of flue gas recirculation ratio on the molar percentage of oxygen in the exhaust gas. Compared to the NGCC power plant without flue gas recirculation, the molar percentage of carbon dioxide in the flue gas increases from 5% to 9.2% and the molar percentage of oxygen decreases from 10.9% to 3.5%. Since energy efficiency is the key parameter of energy conversion systems, the impact of the flue gas recirculation on the different energy inputs and outputs and the overall efficiency of the power plant are also investigated. It is found the positive effects of the flue gas recirculation on the electricity produced by the steam turbine generator (STG) are more important than its cooling effects on the power output of the combustion turbine generator (CTG). The flue gas recirculation has no effects on the water pump of the steam cycle and the increase of energy consumed by the compressor of flue gas is compensated by the decrease of energy consumed by the compressor of fresh air. Based on the Low heating value (LHV) of the natural gas, the flue gas recirculation increases the overall efficiency of the power plant by 1.1% from 57.5% from to 58.2%.

Highlights

Global climate change is arguably the most challenging environmental problem the world will be facing in coming decades and centuries
The main objective of this investigation is to obtain an optimum value for the flue gas recirculation ratio in a 620 MW-Natural Gas Combined Cycle (NGCC) power plant with a 100% excess air in order to have a composition of the exhaust gas suitable for an effective absorption by amine solutions
Compared to the NGCC power plant without flue gas recirculation, the molar percentage of carbon dioxide in the flue gas increases from 5% to 9.2% and the molar percentage of oxygen decreases from 10.9% to 3.5%

Summary

Introduction

Global climate change is arguably the most challenging environmental problem the world will be facing in coming decades and centuries. The main source of global warming is the electricity production that generates the largest share of greenhouse gas emissions as 67% of global electricity production comes from burning fossil fuels, mostly coal and natural gas [1]. The Carbon Capture & Storage (CCS) is included as an integral part of all climate change mitigation strategies proposed by the Intergovernmental Panel on Climate Change (IPCC) and International Energy Agency (IEA). CCS is a good and viable option for reducing CO2 emissions because it can be implemented on a large scale. According to some published data, 70% to 80% of the operating cost of a CCS plant is due to the large amount of energy needed during the capture of CO2 from power generation plants using the available technologies [2]

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